Various exterior elements have been proposed to be added to conventional shackle-equipped padlocks to deter burglars and thieves. In the following U.S. patents, shields have been added to conventional shackle-equipped padlocks to obstruct the U-shaped working area after the shackle has been closed and locked, vis. U.S. Pat. No. 3,475,931, D. J. Foote, U.S. Pat. No. 3,453,846, R. L. Owen, U.S. Pat. No. 4,238,941, D. Halopoff.
However, by obstructing the working area, experience has shown that movement of the padlock about a fixed object such as a hasp, is inhibited. Consequently, inserting and removing a key to release the key tumbler can be difficult.
A more recent padlock design of which I am aware (U.S. Ser. No. 22,399 for "PUSH-BUTTON PADLOCK WITH SECONDARY KEY" filed Mar. 16, 1987, assigned to the assignee of the instant application and incorporated herein by reference), uses a different form of tumbler-latching mechanism. The tumbler cylinder is transverse (not parallel) to the shackle socket openings. Also, a single parallel pin is designed to move in synchronism with rotation with the tumbler to clear a single-keeper notch with the longer shackle leg.
While padlocks set forth above have many advantages, there is need to increase their capability to withstand pry forces at the shackle crown without inhibiting padlock operations.